The present invention relates to a process for applying or removing materials to and from substrates using a scanning probe microscope (SXM), operated at atmospheric pressure. The SXM which may be a scanning tunneling microscope (STM), a scanning force microscope (SFM) or a scanning near-field microscope (SNOM).
It is known to use scanning tunneling microscopes for lithography. In this case, existing resist layers or metal surfaces in air are illuminated by ions or electrons or are oxidized, and fine structures are thus produced (Matsumoto, M. Ishii, K. Segawa: J. Vac. Sci. Technol. Vol. 14(2), 1331 (1996); E. A. Dobisz, C. R. K. Marrian: Appl. Phys. Lett. 58(22), 2526 (1991)). When there is sufficient water content in the ambient air, that is to say, given a humidity of more than 15%, and depending on the polarity of the tip, the illumination is effected with hydronium or hydroxyl ions (H. W. P. Koops, E. A. Dobisz, J. Urban: J. Vac. Sci. Technol. Vol. 15(4), 1369 (1997); E. A. Dobisz, H. W. P. Koops, F. K. Perkins: Appl. Phys. Lett. 68(22), 3653 (1996); A. R. Anway, Field Ionization of Water, The Journal of Chemical Physics, Vol.50, (1969) 2012-2021). In dry ambient air, illumination with electrons can be achieved.
It is also known to use scanning tunneling microscopes for applying material to a substrate. In this case, atoms of the substrate are displaced on the substrate, or the material is applied by transferring probe material by field evaporation (R. Gomer, IBM J. Res. Develop. 30, 428 (1986)).
Also known is to use scanning tunneling microscopes for high-resolution structuring processes and for information storage processes (S. C. Minne, Ph. Flueckinger, H. T. Soh, C. F. Quate: J. Vac. Sci. Technol. Vol. 13, 1380 (1995)).
It is also known to operate scanning tunneling microscopes for deposition lithography under vacuum conditions. In this case, material is supplied from a Knudsen cell, i.e., a reservoir with constriction of the delivery through a cannula or a nozzle (M. A. McCord, D. P. Kern, T. H. P. Chang: J. Vac. Sci. Technol. Vol. 6, 1877 (1988); E. E. Ehrichs, W. F. Smith, A. L . DeLozanne: Ultramicroscopy 42-44, 1438 (1992)). Organometallic compounds and substrates with unprepared surfaces are used.
Furthermore, it is known to carry out the process of electrolysis with an STM or SFM (JP 06 297252 A, JP 05 288714 A). In so doing, the ions contained in a liquid electrolyte are fixed by the electric field to a sample placed in the electrolyte.
These prior processes suffer from a number of disadvantages. It is particularly disadvantageous that it is necessary to work under vacuum conditions, which necessitates high expenditure in terms of equipment and time. Also disadvantageous is the fact that the conductivity of the deposits is usually inadequate because of the great carbon content. Since the known procedure is a serial process, the process is a relatively slow one. Furthermore, only small areas, typically 100 xcexcmxc3x97100 xcexcm at most, are writable. The high degree of probe wear is also disadvantageous.
An object of the present invention is to provide a method which allows effective application or removal of materials to and from substrates using a scanning probe microscope operated at atmospheric pressure.
In the method according to the present invention the substrate is placed in a trough, located on the x-y table, of a scanning probe microscope (SXM), which may be a scanning tunneling microscope, a scanning force microscope or a scanning near-field microscope, and the trough is filled with a liquid and/or gaseous medium up to a level such that the top side of the substrate is covered with a thin layer made of at least one monolayer of the medium. For depositing a structured precipitate from the medium or for the structuring etching of the substrate surface, the microtip of the SXM is then dipped into the layer and supplied with an electric voltage or with voltage pulses.
According to the invention, organometallic or other inorganic and organic compounds are used as the liquid and/or gaseous medium.
The invention present provides for supplying the medium in a quantitatively controlled manner. This may expediently be carried out with the use of weight and density differences existing between the ambient air and the medium, or with the assistance of a pump and controlled valve.
In doing this, the air in the trough will form a lower layer in response to the feeding of the gaseous medium which has a greater molecular weight than the air.
A thermoelectric sensor array or a reflection interferometer, composed of a light source, beam guide, line detector and evaluation electronics, or a total reflector with linear detector may expediently be used for monitoring the level of the medium.
According to the present invention, the medium may be changed during the production of the structured precipitate or during the structuring etching.
The etching products produced during the structuring etch removal are expediently transported away from the surface of the substrate by a rinsing medium.
For the application or removal of larger structure fields and for the three-dimensional construction of nanostructures with the SXM, according to the invention, one or more SXM probe cantilevers having a plurality of microtips may be used, the simultaneous use of all the microtips being ensured by a resistor built into each microtip or by active current control of the individual microtip.
When an SXM probe cantilever having a plurality of microtips is employed, use is also made of a test tip which is utilized as a positioning guide for this SXM probe cantilever during the application or removal of the material, for observation of larger structure fields and/or for three-dimensional processing of nanostructures.
According to the present invention, Me2Au(tfac) (dimethylgold trifluoroacetylacetonate), Me2Au(hfac) (dimethylgold hexafluoroacetylacetonate), Me2Au(acac) (dimethylgold acetylacetonate), CpPt (CH3)3 (cyclopentadienyl platinum trimethyl), Mo(CO)6 (molybdenum hexacarbonyl), Cu(hfac)2 (copper dihexafluoroacetylacetonate) may be used as the organometallic compound.
The present invention provides for the use of TiI4 (titaniumiodite) or TiCl4 (titaniumchloride) as the inorganic compound.
In the case of etch removal, XeF2 (xenondifluoride), TiI4 (titaniumiodite), TiCl4 (titaniumchloride), WF6 (tungstenhexafluoride) or other highly fluorinated or halogenated compounds may be used as the medium.
The present invention also relates to the use of the method according to the present invention for characterization of the geometry and restoration or production of microtips of SXM cantilevers, a tip that is electrically contacted to a conductor track being arranged in the trough on a substrate, and with its aid the geometry of the microtip being scanned by scanning microscopy, or with its aid, restoration or production of a microtip being carried out by supplying an electric voltage or voltage pulses to the contacted tip in order to deposit a precipitate from the medium onto the SXM probe cantilever.
To this end, the polarity of the bias voltage of the SXM, used when depositing a precipitate on the substrate or when etching the substrate, is simply reversed. This results in a material application or an etching of the microtip of the SXM probe cantilever. The polarity of the bias voltage of the SXM can subsequently be reversed again, to then continue to deposit or etch on the substrate.
The present invention also relates to the use of the method according to the present invention to store information, to read information and to erase information, where using the process, molecules or molecular clusters which are suitable as information carriers are applied to the substrates in order to store information, are detected in order to read information, and are removed or restructured in order to erase information.
In this case, according to the present invention, a plurality of tips may be used, repaired or else cleaned in the same way, but also in a mutually independent way.
In the method according to the present invention, individual gas atoms adsorbed at the surface of the substrate or of the microtip of the SXM are decomposed, caused by the use of the gaseous medium. A portion of them, and specifically metal atoms having carbon residues, are deposited on the surface of the substrate or of the microtip, or an etching of the substrate or of the microtip is carried out. It is virtually about a CVD process (chemical vapor deposition process), while dispensing with the vacuum necessary for the customary CVD by creating a local precursor atmosphere utilizing the particular material property of the precursor (high vapor pressure, greater density than air).
In contrast, in the electrolysis process of Japanese Patent Document Nos. JP 06 297252 A and JP 05 288714 A mentioned above, using an STM or SFM, work is done with a liquid medium, namely, an electrolyte. There a completely different process principle than for the CVD of the present invention is employed. While in the case of the electrolysis, the ions contained in the electrolyte are fixed by the electrical field to the substrate, in the method according to the present invention, a deposition induced by electron beam or ion beam is carried out.
The method according to the present invention has the particular distinction that it is not necessary to work under costly vacuum conditions. It is also advantageous that highly conductive deposits can be used, and that by rapid changing of the precursors, different processes such as deposition and etching can be carried out in a simple manner one after the other. Another advantage is that the probes which become worn when the process is being carried out can be regenerated again using the same process.